Friction stir welding (FSW) is commonly used to weld two or more work pieces formed of various metals, such as aluminum, magnesium, copper, titanium, steel and the like, one to another. FSW techniques may be employed satisfactorily to form welded lap joint, L-joint and/or T-joint.
During conventional FSW processes (including continuous and segmented friction stir welding), a FSW tool having a specific geometry is forced into, and traversed through the material to be welded. The key structural components of the tool include a shoulder and pin (sometimes called a “probe” in art parlance) extending outwardly from the shoulder. During the FSW process, the pin travels physically in and through the material along a joint line, while the shoulder is in surface contact with the material. Heat is generated by the tool shoulder by virtue frictional rubbing on the material surface it is in contact with and by virtue of the pin mixing the molten material below the shoulder. This mixing action of the molten material during the FSW process permits the material to be transferred across the joint line which forms a stirred region. Process variables affecting the FSW process may include rotation and travel speeds, tool design, orientation, position and tool forging load.
On prior FSW technique proposed in U.S. Pat. No. 7,225,966 (the entire content of which is expressly incorporated hereinto by reference) including forming an aircraft component with a weld joint by application of a sealant layer to the surfaces to be joined. Such sealant is then cured in place by the elevated temperatures resulting from the FSW process.
U.S. Pat. No. 7,240,821 refers to a method for weldbonding at least two work-pieces wherein an adhesive is applied to a first surface of a first work-piece which is then brought into contact with a surface of a second work-piece. The first and second work-pieces are then friction stir or friction stir spot welded together which cures the adhesive. According to the technique in the '821 patent, the use of bonding tools to maintain the two work-pieces together during curing of the adhesive is eliminated.
In the prior art FSW techniques, however, a relatively small-sized weld region (sometimes referred to as a “weld nugget” in art parlance) is obtained having gaps on both sides of thereof. This occurs due to the fact that the tool shoulder must be in intimate contact the upper region of one of the workpieces and the existence of an orthogonal plane associated with such workpiece and also due the physical characteristics of the tool and its required movements in order to achieve the weld nugget. As such, conventional FSW processes are limited to providing weld regions at only certain locations relative to the workpieces to be joined, for example, typically at a center flange portion associated with the upper workpiece.
It would therefore be desirable if larger sized weld regions could be formed by means of FSW processes so as to allow for greater welding between workpieces than can be achieved by conventional FSW processes. It would also be highly desirable if a substantial part of one of the workpieces could be eliminated thereby providing substantial weight savings for applications in which component weight is a significant factor (e.g., as in the fabrication of aircraft components). It is towards fulfilling such needs that the present invention is directed.